Recently, much attention has been focused on III-V nitride-based semiconductors, and particularly GaN-based semiconductors, for blue, green, and ultraviolet light emitting diode (LED) applications. One important reason is that GaN-based LEDs have been found to exhibit efficient light emission at room temperature.
In general, GaN-based LEDs comprise a multilayer structure in which n-type and p-type GaN-based semiconductor layers are stacked on a substrate (most commonly on a sapphire substrate with the n-type GaN-based semiconductor layer in contact with the substrate), and a light-transmissive metal electrode layer is formed over the p-type semiconductor layer. In certain embodiments, an active region (which can be a single or multiple quantum well structure, for example) is disposed between the p-type and n-type semiconductor layers. In general, each of the layers of the multilayer structure has a four-sided planar top surface.
Because the substrate is normally comprised of an electrically insulative material, such as sapphire, the p-side and the n-side electrical contacts are normally both made on the top side of the device. In general, a portion of the top side of the device is etched to expose one corner or edge of the n-type semiconductor layer, and an n-electrode (i.e. bonding pad) of a suitable metallic material is deposited on the exposed corner or edge of the n-type semiconductor layer. The p-side contact is made by forming a bonding pad of a metallic material on the top surface of the light-transmissive p-electrode layer.